GB2564550B - Non-contiguous channel usage in multi-channel wireless networks - Google Patents

Description

NON-CONTIGUOUS CHANNEL USAGE IN MULTI-CHANNEL WIRELESS NETWORKS

FIELD OFTHE INVENTION

The present invention relates generally to communication networks and more specifically to methods and devices for transmitting data over a wireless communication network using Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), the network being accessible by a plurality of stations.

BACKGROUND OF THE INVENTION

Wireless local area networks (WLANs), such as a wireless medium in a communication network using Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), are founded on the principles of collision avoidance. Such networks may also conform to a communication standard such as a communication protocol of 802.11 type e.g. Medium Access Control (MAC).

The IEEE 802.11 MAC standard defines the way WLANs must work at the physical and medium access control (MAC) level. Typically, the 802.11 MAC (Medium Access Control) operating mode implements the well-known Distributed Coordination Function (DCF) which relies on a contention-based mechanism based on the so-called “Carrier Sense Multiple Access with Collision Avoidance” (CSMA/CA) technique.

The 802.11 medium access protocol standard or operating mode is mainly directed to the management of communication nodes waiting for the medium to become idle so as to try to access to the medium.

The network operating mode defined by the IEEE 802.11ac standard provides very high throughput (VHT) by, among other means, moving from the 2.4GHz band which is deemed to be highly subject to interference to the 5GHz band, thereby allowing for wider frequency contiguous channels of 80MHz, two of which may optionally be combined to get a 160MHz channel as operating band ofthe wireless network.

The 802.11ac standard also tweaks Clear Channel Assessment (CCA) method to allow for composite channels of varying and predefined bandwidths of 20, 40 or 80MHz, the composite channels being made of one or more contiguous sub-channels within the operating band. The 160MHz composite channel is made possible by the combination of two 80MHz composite channels within the 160MHz operating band. A composite channel therefore consists of a primary channel and at least a secondary channel of for example 20MHz each. The primary channel is used by the communication nodes to sense, using CCA, whether or not the channel is idle, which channel can thus be extended using the secondary channel to form a composite channel.

Tertiary and quaternary channels may also take part of the composite channel. A station is allowed to use as much channel capacity (or bandwidth, i.e. of sub-channels in the composite channel) as is available from the primary channel. The constraint is that the combined channels need to be contiguous for a station with a single antenna station (or single spatial stream).

The station may thus use the combined channels as a 40 or 80 or 160MHz modulation band for data modulation when transmitting data.

However, if there is noise or interference on one of the 20MHz channel within the wider composite channel, the available bandwidth is reduced. The 802.11ac standard only allows a restricted number of composite channel configurations, i.e. of predefined subsets of 20MHz channels that can be reserved and used by the 802.11ac stations as modulation band to transmit data. These are contiguous channels of 20, 40, 80MHz bandwidth, each including the primary channel, in case of single antenna devices.

Therefore, noise or interference even on a small portion of the composite channel may substantially reduce the available bandwidth of the composite channel to only 40 or 20 MHz, since the resulting reserved bandwidth must meet the 20MHz, 40MHz, 80MHz or 160MHz channel configurations allowed by the standard.

More recently, Institute of Electrical and Electronics Engineers (IEEE) officially approved the 802.11 ax task group, as the successor of 802.11ac. The primary goal of 802.11ax consists to improve data speed for devices used in dense deployment scenarios.

The huge gigabit throughputs that are often attributed to 802.11 ac are mainly theoretical. In fact, they represent the overall capacity a Wi-Fi network can support, for instance 1.3 Gbps in today’s most advanced routers. However, they can occur only in the rarest circumstances where any individual device would actually be able to connect at such high rates.

The existing 802.11ac standard requires that the composite channel width be specified in the 802.11ac frames, resulting in that channels non-contiguous within the operating band cannot be used although they are available. Therefore, in the 802.11 ax research context, there is a need to enhance the efficiency and usage of the wireless channel.

Publication IEEE 802.11-13/1058r0 “Efficient Wider Bandwidth Operation” provided during the 802.11ax task group has raised the benefit of using all available channels, even if no solution to do so has been provided.

SUMMARY OF INVENTION

It is a broad objective of the present invention to provide communication methods and devices for transmitting data over an (ad-hoc) wireless network, the physical medium of which being shared between a plurality of communication nodes, often containing a single antenna device.

The present invention has been devised to overcome the foregoing limitations.

In this context, the invention provides a communication apparatus according to Claim 1.

The apparatus comprises: determination means for performing carrier sensing on a successive plurality of sub-channels to thereby determine an available sub-channel to be used to transmit data; and transmission means for transmitting to another apparatus, a physical layer preamble of data to transmit, the physical layer preamble including information related to a sub-channel that is not available for performing data transmission based on a result of the determination obtained by the determination means.

Correlatively, the invention provides a corresponding method of communicating.

The method comprises: performing carrier sensing on a successive plurality of sub-channels to thereby determine an available sub-channel to be used to transmit data; and transmitting to another apparatus, a physical layer preamble of data including information related to a sub-channel that is not available for performing data transmission based on a result of the determination obtained by the determination means.

Optional features of embodiments of the invention are defined in the appended claims.

In embodiments, the communication apparatus further comprises storing means for storing the information in the physical layer preamble of data prior to transmission.

In other embodiments, the transmission means are further configured for transmitting data to the other apparatus, said transmitting including modulating the data on a modulation band encompassing two or more available sub-channels as determined by the determination means.

In specific embodiments, the two or more available sub-channels are made of sub-channels that are not contiguous within the successive plurality of sub-channels.

In other specific embodiments, an operating mode of the wireless network defines a restricted number of predefined sub-channel subsets that are available for reservation by any wireless node of the wireless network to transmit data, the predefined sub-channel subsets being made of contiguous sub-channels within the successive plurality of sub-channels, and the two or more available sub-channels encompassed by the modulation band form a sub-channel subset different from any predefined sub-channel subset.

According to a specific feature, the operating mode of the wireless network is according to the 802.11ac standard, and the restricted number of predefined subchannel subsets is made of 20MHz, 40MHz, 80MHz and optionally 160MHz contiguous bandwidths within the successive plurality of sub-channels.

In yet other specific embodiments, the two or more available sub-channels are made of sub-channels that are contiguous within the operating band.

In yet other embodiments, a map field in the physical layer preamble includes a sub-channel map defining available sub-channels for performing data transmission and the sub-channel that is not available for performing data transmission.

In specific embodiments, the map field includes a map identifier identifying an entry of a table of maps.

In other specific embodiments, the map field starts a HE-SIG-A header in the physical layer preamble in accordance with the 802.11 ax standard.

In yet other embodiments, performing carrier sensing includes using a clear channel assessment mechanism to sense available sub-channels within the successive plurality of sub-channels.

In yet other embodiments, performing carrier sensing includes determining a first set of sub-channels that are sensed idle within the successive plurality of sub- channels and reducing the first set to a set of available sub-channels to perform data transmission.

In yet other embodiments, the transmission means are further configured for modulating the physical layer preamble on a primary sub-channel determined as available based on a result of the determination and duplicating the modulated preamble on a secondary sub-channel determined as available based on a result of the determination.

In embodiments, the transmission means are further configured for modulating the data on the modulation band by turning off one component of a modulation scheme that correspond to the sub-channel that is not available.

According to some features, the transmission means are further configured for transmitting the information related to the sub-channel that is not available from a MAC layer to a PHY layer of the communication apparatus, using a MAC-PHY interface, to configure the PHY layer with the information for the PHY layer to perform modulation on the modulation band.

Also, the information may be passed to the PHY interface as a parameter of a PHY primitive.

In some embodiments, the modulation band is made of all the sub-channels of the successive plurality of sub-channels from the first sub-channel determined as available by the determination means to the last sub-channel determined as available by the determination means.

In some embodiments, the modulation band is the successive plurality of sub-channels.

In yet other embodiments, the communication apparatus is further configured to, prior to performing carrier sensing, determining whether or not the communication apparatus supports transmission over a subset of sub-channels different from predefined subsets or supports transmission over non-contiguous sub-channels within the successive plurality of sub-channels.

The invention also relates to a non-transitory computer-readable medium storing a program which, when executed by a microprocessor or computer system in a communication apparatus, causes the apparatus to perform any method as defined above.

The non-transitory computer-readable medium may have features and advantages that are analogous to those set out above and below in relation to the methods and node devices.

At least parts of the methods according to the invention may be computer implemented. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit", "module" or "system". Furthermore, the present invention may take the form of a computer program product embodied in any tangible medium of expression having computer usable program code embodied in the medium.

Since the present invention can be implemented in software, the present invention can be embodied as computer readable code for provision to a programmable apparatus on any suitable carrier medium. A tangible carrier medium may comprise a storage medium such as a floppy disk, a CD-ROM, a hard disk drive, a magnetic tape device or a solid state memory device and the like. A transient carrier medium may include a signal such as an electrical signal, an electronic signal, an optical signal, an acoustic signal, a magnetic signal or an electromagnetic signal, e.g. a microwave or RF signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the present invention will become apparent to those skilled in the art upon examination of the drawings and detailed description. Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings.

Figure 1 illustrates a typical wireless communication system in which embodiments of the invention may be implemented;

Figure 2 is a timeline schematically illustrating a conventional communication mechanism according to the IEEE 802.11 standard;

Figure 3a illustrates 802.11ac channel allocation that support channel bandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz as known in the art;

Figure 3b illustrates an example of 802.11ac multichannel station using a transmission opportunity on an 80 MHz channel as known in the art;

Figure 4 shows a conceptual diagram illustrating a broadband channel usage mechanism employing an 80MHz channel bandwidth as known in the art;

Figure 5 illustrates three examples of dynamic fallback to narrower channel widths in the presence of co-channel interference or noise that only affects a portion of the larger channel;

Figure 6 shows a schematic representation a communication device or station in accordance with embodiments of the present invention;

Figure 7 shows a schematic representation of a wireless communication device in accordance with embodiments of the present invention;

Figure 8 illustrates exemplary communication timeline illustrating embodiments of the invention;

Figures 9 and 10 illustrate a typical 802.11ac frame format as known in the art;

Figure 11 illustrates an 802.11 ax frame format;

Figures 12a and 12b illustrate an adaptation of the 802.11ax frame format of Figure 11 to embodiments of the invention;

Figures 13a and 13b illustrate, using flowcharts, general steps of an enhanced channel usage method for multi-channel transmission to an 802.11 wireless medium, that allows usage of non-contiguous sub-channels, in accordance with embodiments of the present invention; and

Figure 14 illustrates, using a flowchart, general steps of the enhanced channel usage method of Figures 13a and 13b from the receiving node’s perspective.

DETAILED DESCRIPTION

The invention will now be described by means of specific non-limiting exemplary embodiments and by reference to the figures.

Figure 1 illustrates a communication system in which several communication nodes exchange data frames over a radio transmission channel 100 of a wireless local area network (WLAN).The radio transmission channel 100 is defined by an operating band, for instance with a bandwidth available for the communication nodes.

Access to the shared radio medium to send data frames is based on the CSMA/CA technique, for sensing the carrier and avoiding collision by separating concurrent transmissions in space and time.

Carrier sensing in CSMA/CA is performed by both physical and virtual mechanisms. Virtual carrier sensing is achieved by transmitting control frames to reserve the medium prior to transmission of data frames.

Next, a transmitting or source node first attempts through the physical mechanism, to sense a medium that has been idle for at least one DIFS (standing for DCF InterFrame Spacing) time period, before transmitting data frames.

However, if it is sensed that the shared radio medium is busy during the DI FS period, the source node continues to wait until the radio medium becomes idle. To do so, it starts a countdown backoff counter designed to expire after a number of timeslots, chosen randomly between [0, CW], CW (integer) being referred to as the Contention Window. This backoff mechanism or procedure is the basis of the collision avoidance mechanism that defers the transmission time for a random interval, thus reducing the probability of collisions on the shared channel. After the backoff time period, the source node may send data or control frames if the medium is idle.

One problem of wireless data communications is that it is not possible for the source node to listen while sending, thus preventing the source node from detecting data corruption due to channel fading or interference or collision phenomena. A source node remains unaware of the corruption of the data frames sent and continues to transmit the frames unnecessarily, thus wasting access time.

The Collision Avoidance mechanism of CSMA/CA thus provides positive acknowledgement (ACK) of the sent data frames by the receiving node if the frames are received with success, to notify the source node that no corruption of the sent data frames occurred.

The ACK is transmitted at the end of reception of the data frame, immediately after a period of time called Short InterFrame Space (SIFS).

If the source node does not receive the ACK within a specified ACK timeout or detects the transmission of a different frame on the channel, it may infer data frame loss. In that case, it generally reschedules the frame transmission according to the above-mentioned backoff procedure. Even if this can be seen as a bandwidth waste if only the ACK has been corrupted but the data frames were correctly received by the receiving node, this basic mechanism is well fitted for small frames that are quite common in usual traffic.

Figure 2 illustrates the behaviour of three groups of nodes during a conventional communication over a 20 MHz channel ofthe 802.11 medium: transmitting or source node 20, receiving or addressee or destination node 21 and other nodes 22 not involved in the current communication.

Upon starting the backoff process 270 prior to transmitting data, a station e.g. source node 20, initializes its backoff time counter to a random value as explained above. The backoff time counter is decremented once every time slot interval 260 for as long as the radio medium is sensed idle (countdown starts from TO, 23 as shown in the Figure).

The time unit in the 802.11 standard is the slot time called ‘aSlotTime’ parameter. This parameter is specified by the PHY (physical) layer (for example, aSlotTime is equal to 9ps for the 802.11η standard). All dedicated space durations (e.g. backoff) add multiples of this time unit to the SIFS value.

The backoff time counter is ‘frozen’ or suspended when a transmission is detected on the radio medium channel (countdown is stopped at T1, 24 for other nodes 22 having their backoff time counter decremented).

The countdown of the backoff time counter is resumed or reactivated when the radio medium is sensed idle anew, after a DIFS time period. This is the case for the other nodes at T2, 25 as soon as the transmission opportunity (transmission 230 of data and reception of acknowledgment 240) used by source node 20 ends and the DIFS period 28 elapses. DIFS 28 (DCF inter-frame space) thus defines the minimum waiting time for a source node before trying to transmit some data. In practice, DIFS = SIFS + 2 * aSlotTime.

When the backoff time counter reaches zero (26) at T1, the timer expires, the corresponding node 20 starts sending data (230) on the medium using a data frame, and the backoff time counter is reinitialized using a new random backoff value.

An ACK frame 240 is sent by the receiving node 21 after having correctly received the data frame sent, after a SIFS time period 27.

If the source node 20 does not receive the ACK 240 within a specified ACK Timeout (generally within the maximum value for a transmission opportunity TXOP), or if it detects the transmission of a different frame on the radio medium, it reschedules the frame transmission using the backoff procedure anew.

Since the DIFS value is higher than the SIFS value, other nodes 22 cannot decrement their backoff counter between the data transmission 230 and the corresponding Ack transmission 240. As a consequence, access to the radio medium for the other nodes 22 is consequently deferred (the medium is seen as busy 290) until the next backoff countdown period starts at T2.

This prevents the listening nodes 22 from transmitting any data during period 230-240.

The 802.11 backoff procedure was first introduced for the DCF mode as the basic solution for collision avoidance, and further employed by the IEEE 802.11e standard to solve the problem of internal collisions between enhanced distributed channel access functions (EDCAFs). In the emerging IEEE 802.11n/ac/ax standards, the backoff procedure is still used as the fundamental approach for supporting distributed access among mobile stations or nodes.

The rapid growth of smart mobile devices is driving mobile data usage and 802.11 WLAN proliferation, creating an ever-increasing demand for faster wireless networks to support bandwidth-intensive applications, such as web browsing and video streaming. The new IEEE 802.11ac standard is designed to meet this demand, by providing major performance improvements over previous 802.11 generations.

The IEEE 802.11ac standard is an emerging very high throughput (VHT) wireless local access network (WLAN) standard that can achieve physical layer (PHY) data rates of up to 7 Gbps for the 5 GHz band.

The scope of 802.11ac includes single link throughput supporting at least 500 Mbps, multiple-station throughput of at least 1 Gbps and backward compatibility and coexistence with legacy 802.11 devices in the 5 GHz band.

Consequently, this standard is targeted at higher data rate services such as high-definition television, wireless display (high-definition multimedia interface - HDMI -replacement), wireless docking (wireless connection with peripherals), and rapid sync-and-go (quick upload/download).

In general, 802.11ac could be schematized as an extension of IEEE 802.11η in which the two basic notions of multiple-input, multiple-output (ΜΙΜΟ) and wider channel bandwidth are enhanced for greater efficiency.

Using the optional ΜΙΜΟ feature, an access point AP (having multiple antennae) may communicate with several nodes simultaneously using Spatial Division Multiple Access (SDMA). SDMA multiple access scheme enables multiple streams transmitted to different receiving nodes at the same time to share the same frequency channel but requires several antennas.

Contrary to 802.11η in which each communication node should support up to two spatial streams (SSs) and an operating band of 40 MHz bandwidth, only one spatial stream (and thus only one antenna par device) is required in 802.11ac or 802.11ax, while operating bands of 80MHz or 160MHz bandwidth are allowed. In 802.11ac or 802.11 ax, the single antenna of the node is able to modulate on or demodulate from such 80MHz or 160MHz band, referred to as modulation band in the description below.

One reason for such a change in the new versions of 802.11 is that increasing the number of antennas often results in higher cost. Indeed, supporting multiple Spatial Streams (SS) has been considered as requiring at least the same number of antennas (and as much reception chains behind these antennas), thus important costs. Consequently, a majority of 802.11η devices available on the market could only support a single SS.

In 802.11ac, support for only one SS is required so that devices, and especially smartphones, could be labelled as ‘802.11ac compliant’. The operating mode with an 80 MHz operating band is made mandatory as a lower cost alternative to the two SS and 40 MHz operating band. Hence, the operating modes that utilize more than one spatial stream are now become optional in 802.11ac.

As a result, 802.11ac is targeting larger bandwidth transmission through multi-channel operations, meaning that the single antenna of the nodes modulates on or demodulates from a modulation band that can be made of one or more 20MHz channels, for instance 40MHz or 80MHz or even 160MHz. The wider channel aspect is further described in regards to Figures 3 and Figure 4.

In order to support wider (i.e. more than 20MHz) modulation bands within the operating band, the operating band in 802.11ac is made of an ordered succession (or series) of sub-channels as shown for instance in Figure 3a. IEEE 802.11ac introduces support of a restricted number of predefined subsets of these sub-channels to form the sole predefined composite channel configurations that are available for reservation by any 802.11ac node on the wireless network to transmit data.

The predefined subsets are shown in the Figure and correspond to 20 MHz, 40 MHz, 80 MHz, and 160 MHz channel bandwidths that include the primary channel, compared to only 20 MHz and 40 MHz supported by 802.11η. Indeed, the 20 MHz component channels (or sub-channels) 300-1 to 300-8 are concatenated to form wider communication composite channels on/from which the nodes modulate/demodulate data.

In the standard, the sub-channels of each predefined 40MHz, 80MHz or 160MHz subset are contiguous within the operating band, i.e. no hole (i.e. missing subchannel) within the sub-channels as ordered in the operating band is allowed.

The 160 MHz channel bandwidth is composed of two 80 MHz channels that may or may not be frequency contiguous. The 80 MHz and 40 MHz channels are respectively composed of two frequency adjacent or contiguous 40 MHz and 20 MHz channels, respectively. The support of 40 MHz and 80 MHz channel bandwidths is mandatory while support of 160 MHz and 80 + 80 MHz is optional (80+80 MHz means that a multi-channel is made of two frequency non-contiguous channels having a bandwidth of 80 MHz). A multichannel communication node (accessing an 80 MHz operating band in the illustrated example of Figure 3b) accesses the wireless medium for a new transmission opportunity TxOP, through the enhanced distributed channel access (EDCA) mechanism on the “primary channel” (300-3). Indeed, for each channel bandwidth, 802.11ac designates one channel as “primary,” meaning that it is used for transmission at that bandwidth. It shall, however, transmit an 80 MHz PPDU (PPDU means PLCP Protocol Data Unit, with PLCP for Physical Layer Convergence Procedure; basically a PPDU refers to an 802.11 physical frame) only after the CCA (Clear Channel Assessment) process, meaning that the data are modulated on the 80MHz modulation band.

Figure 4 gives a description of the CCA process for an 80Mhz composite channel. During the CCA, all the sub-channels that should be used in the aggregated channel are sensed (the signal and energy levels are evaluated, and a channel is considered as idle if the energy level measured on the channel is lower than the CCA threshold of -62dBm and the signal is lower than -82dBm on the primary channel, and -72dBm on the secondary channels).

If all secondary channels have been idle for at least a point coordination function (PCF) inter-frame spacing (PIFS), with PIFS = SIFS + aSlotTime, then the secondary channels can also be used. If at least one of the secondary channels has not been idle for a PIFS, then the node must either restart its backoff count, or use the current TxOP for 40 MHz or 20 MHz PPDUs.

The vertical aggregation scheme of Figure 3b reflects the extension of the payload 230 to all sub-channels, i.e. the modulation of data on the whole 80MHz modulation band. If there is only one collision in one of the channels at a given time, the risks of having a corrupted segment of these sequences are very high despite the error-correcting decoding process. All MPDU (MAC Protocol Data Unit) frames inside the PPDU could thus automatically be considered as incorrect.

In the description below, the words “channel, “20 MHz channel or “subchannel mainly refer to the same technical feature, i.e. any channel that complies with 802.11n or older standards. “Composite channel" thus refers to the additional feature of 802.11ac in which a composite channel is made of one or more sub-channels that are contiguous within the operating band of the wireless network. In 802.11ac, the composite channels are 20MHz wide (if made of only one sub-channel) or 40MHz wide or 80MHz wide or, optionally, 160MHz wide.

Further, Figure 4 gives a description of the CCA process allowing the usage of wide bandwidth. During the backoff countdown period 260, source node STA1 20 senses all the channels forming a wider bandwidth. When the backoff counter reaches 0 (26-1), if the secondary channel have been idle for at least a PIFS period, they are considered idle and can be aggregated and used to modulate data 230-1 on a wider channel (in the example of the left-side part of the Figure, a 80Mhz channel).

If during the PIFS period, the secondary channel is not idle (for instance as in the right-side part of the Figure where the backoff counter of source node STA1 20 reaches zero at 26-2), source node STA1 can decide to either restart its backoff counter, or try to use a 40Mhz channel and send data 230-2 on this 40Mhz channel (using a longer airtime).

The ability of the 802.11ac nodes to fall back to lower bandwidth modes, and thus to narrower modulation band for transmission, in case not all the targeted bandwidth is available is known as a fallback mechanism.

As addressed above, the IEEE 802.11ac standard enables up to four, or even eight, 20 MHz channels to be bound. Because of the limited number of channels (19 in the 5 GHz band in Europe), channel saturation becomes problematic. Indeed, in densely populated areas, the 5 GHz band will surely tend to saturate even with a 20 or 40 MHz bandwidth usage per Wireless-LAN cell.

As a result, the fallback mechanism currently provided in the 802.11ac standard is too limitative.

Channel interference (Figure 5) is typically caused by a legacy 802.11a or 802.11η node transmitting on a 20 MHz channel. Indeed, the 802.11ac node may transmit over a fraction of the original wished bandwidth: depending of which 20Mhz channels (300) are busy, the channel width of resulting composite channel is reduced from 80MHz to a predefined channel width of the 802.11ac channel bonding scheme, namely to 40MHz (cases 510 and 511) or to 20Mhz (case 520), whereas a 60Mhz (i.e. additional 20MHz or40MHz respectively) bandwidth is potentially available.

One can note the 802.11ac standard has not envisaged using such lost bandwidth, as the VHT preamble in the 802.11ac frames embeds a bandwidth indication only supporting predefined channel widths and thus predefined modulation bands, namely 20, 40, 80 or 160 Mhz.

This bandwidth allocation deficiency can be especially problematic with personal devices on which a central organization has little or even no control to select the wireless channels of the 5GHz or the like band. This is ascertained in distributed environments, which are by essence not managed at all.

The present invention falls within enhancement of the 802.11ac standard, and more precisely into the context of 802.11 ax wherein dense wireless environments are more ascertained to suffer from previous limitations.

The present invention provides enhanced channel usage methods and devices for data communication over an ad-hoc wireless network, the physical medium of which being shared between a plurality of communication stations (also referred to as nodes or devices).

An exemplary ad-hoc wireless network is an IEEE 802.11ac network (and upper versions) in which an operating band made of an ordered series of sub-channels is used and in which a restricted number of predefined composite channel configurations is available. However, the invention applies to any wireless network in which a source node 101-107 sends data of a data stream to a receiving node 101-107 using multiple channels (see Figure 1). The invention is especially suitable for data transmission in an IEEE 802.11 ax network (and future versions) requiring more flexibility in the bandwidth management.

The behaviour of communication nodes during a conventional communication over an 802.11 medium has been recalled above with reference to Figures 1 to 5.

One aspect of embodiments provides signalling a sub-channel map in a sent data frame, in associating with data of the data frame, and then transmitting the data over the sub-channels indicated (as available) in the sub-channel map, using a modulation of the data on a modulation band that encompasses these sub-channels.

This signalling makes it possible for the receiving node to have knowledge of the sub-channels actually used by the source node, and thus to configure itself to efficiently demodulate from the appropriate modulation band and to retrieve the transmitted data from the demodulated signal for the appropriate sub-channels.

Thanks to the sub-channel map, the source node may decide to use (for transmission of data) any sub-channel configuration, i.e. beyond the 20MHz, 40MHz, 80MHz and 160MHz bands allowed by 802.11ac. For instance, using non-contiguous sub-channels in the operating band is made possible by the invention.

Figure 6 schematically illustrates a communication device 600 of the radio network 100, configured to implement at least one embodiment of the present invention. The communication device 600 may preferably be a device such as a micro-computer, a workstation or a light portable device. The communication device 600 comprises a communication bus 613 to which there are preferably connected: • a central processing unit 611, such as a microprocessor, denoted CPU; • a read only memory 607, denoted ROM, for storing computer programs for implementing the invention; • a random access memory 612, denoted RAM, for storing the executable code of methods according to embodiments of the invention as well as the registers adapted to record variables and parameters necessary for implementing methods according to embodiments of the invention; and • at least one communication interface 602 connected to the radio communication network 100 over which digital data packets or frames are transmitted, for example a wireless communication network according to the 802.11ac protocol. The data frames and aggregated frames are written from a FIFO sending memory in RAM 612 to the network interface for transmission or are read from the network interface for reception and writing into a FIFO receiving memory in RAM 612 under the control of a software application running in the CPU 611.

Optionally, the communication device 600 may also include the following components: • a data storage means 604 such as a hard disk, for storing computer programs for implementing methods according to one or more embodiments of the invention; • a disk drive 605 for a disk 606, the disk drive being adapted to read data from the disk 606 or to write data onto said disk; • a screen 609 for displaying decoded data and/or serving as a graphical interface with the user, by means of a keyboard 610 or any other pointing means.

The communication device 600 may be optionally connected to various peripherals, such as for example a digital camera 608, each being connected to an input/output card (not shown) so as to supply data to the communication device 600.

Preferably the communication bus provides communication and interoperability between the various elements included in the communication device 600 or connected to it. The representation ofthe bus is not limiting and in particular the central processing unit is operable to communicate instructions to any element of the communication device 600 directly or by means of another element of the communication device 600.

The disk 606 may optionally be replaced by any information medium such as for example a compact disk (CD-ROM), rewritable or not, a ZIP disk, a USB key or a memory card and, in general terms, by an information storage means that can be read by a microcomputer or by a microprocessor, integrated or not into the apparatus, possibly removable and adapted to store one or more programs whose execution enables a method according to the invention to be implemented.

The executable code may optionally be stored either in read only memory 607, on the hard disk 604 or on a removable digital medium such as for example a disk 606 as described previously. According to an optional variant, the executable code of the programs can be received by means of the communication network 603, via the interface 602, in order to be stored in one of the storage means of the communication device 600, such as the hard disk 604, before being executed.

The central processing unit 611 is preferably adapted to control and direct the execution of the instructions or portions of software code of the program or programs according to the invention, which instructions are stored in one of the aforementioned storage means. On powering up, the program or programs that are stored in a nonvolatile memory, for example on the hard disk 604 or in the read only memory 607, are transferred into the random access memory 612, which then contains the executable code of the program or programs, as well as registers for storing the variables and parameters necessary for implementing the invention.

In a preferred embodiment, the apparatus is a programmable apparatus which uses software to implement the invention. However, alternatively, the present invention may be implemented in hardware (for example, in the form of an Application Specific Integrated Circuit or ASIC).

The invention is described from now using the example of transmitting data on non-contiguous sub-channels (NCSC). Below it is thus made reference to nodes that support transmission over non-contiguous sub-channels within the operating band, made reference to a flag signalling such ability to support non-contiguous sub-channels for transmission, etc.

However, as introduced above, the invention regards more generally support of transmission over subsets of sub-channels not authorized by some standards, for instance subsets that are different from the subsets predefined in 802.11ac (802.11ac configurations with 20MHz/40MHz/80MHz/160MHz bandwidths). The man skilled in the art would be able to adapt the teachings below to this more general situation.

Figure 7 is a block diagram schematically illustrating the architecture of a communication device also called node (or station) 600 adapted to carry out, at least partially, the invention. As illustrated, node 600 comprises a physical (PHY) layer block 703, a MAC layer block 702, and an application layer block 701. Between PHY block 703 and MAC block 702, node 600 comprises block 706 containing the interface functions (also known as primitives) allowing the communication of data and parameters between the MAC and PHY layers.

The PHY layer block 703 (here an 802.11 standardized PHY layer) has the task of formatting, modulating on or demodulating from the modulation band, and thus sending or receiving frames over the radio medium used 100, such as 802.11 data frames.

The MAC layer block or controller 702 preferably comprises a MAC 802.11 layer 704 implementing conventional 802.11 MAC operations, and an additional block 705 for carrying out, at least partially, the invention. The MAC layer block 702 may optionally be implemented in software, which software is loaded into RAM 612 and executed by CPU 611.

Preferably, the additional block, referred to non-contiguous sub-channel (NCSC) usage module 705, implements the part of the invention that regards node 600, i.e. transmitting operations for a source node, receiving operations for a receiving node and monitoring operations for any other node that is able to understand the signalling flag according to the invention.

From source node’s perspective, NCSC module 705 senses which subchannels, in particular non-contiguous ones, are available for transmission, checks that the receiving node supports using such sub-channels, builds a sub-channel map to be signalled to the receiving node to make it possible for them to exchange data over the selected sub-channels, and informs the PHY layer of which sub-channels are to be used for data transmission.

From receiving node’s perspective, NCSC module 705 retrieves the subchannel map based on the signalling included in the data frames, to control the PHY layer to demodulate from the appropriate modulation band and to retrieve data from the demodulated signal for the appropriate sub-channels (as specified in the sub-channel map).

On top of the Figure, application layer block 701 runs an application that generates and receives data packets, for example data packets of a video stream.

Application layer block 701 represents all the stack layers above MAC layer according to ISO standardization.

Figure 8 shows an exemplary communication line illustrating embodiments of the invention. Although this example shows a WLAN system using a multi-channel including four contiguous sub-channels having a channel bandwidth of 20 MHz, the number of sub-channels or the channel bandwidth thereof may vary.

In this example, the source node transmits data over non-contiguous subchannels within the 80MHz operating band to the receiving node.

An 802.11ac-compliant node having one and a single antenna cannot use channels that are not contiguous or successive within the operating band, according to 802.11ac standard. Recently, paper contribution to 802.11ax has addressed the capability to communicate over a set of channels containing busy channels. The document IEEE 802.11-15/0035r1, entitled “Scalable Channel Utilization Scheme”, proposes a scalable channel utilization scheme to utilize as many channels as possible, even non-contiguous within the operating band, by turning on/off part of the OFDM tones.

Modulation is thus provided on a modulation band that encompasses all the sub-channels that are to be used, and then the OFDM carriers corresponding to non-available sub-channels within the modulation band are cancelled, i.e. their corresponding OFDM components are set to zero.

The OFDM Tones corresponding to a detected busy channel can be turned off so as to cause no interference with the ongoing transmission. For instance, the D(k) component of the following expression (expressing the OFDM signal) can be set to zero: ^(R)=~Σ//(k)expp^' n = θΊ’_ 1 where N is the FFT size.

However, to inform correctly the receiving node of which sub-channels are to be used for data transmission, some additional mechanisms are required as now defined by the present invention.

Indeed, in order for the receiving node to be able to correctly receive (i.e. demodulate) the data transmitted over the non-contiguous sub-channels, the receiving node should know in advance which sub-channels of the operating band and of the modulation band are used and which ones are not used. Thanks to this information, the receiving node will be able to demodulate from the appropriate modulation band and to discard the demodulated signal for the unused sub-channels by setting the appropriate D(k) components to zero in the above formula.

As shown in Figure 8, the CCA mechanism makes it possible to determine that tertiary channel 700-2 is not available. As a consequence, the source station informs its PHY layer that even if one of the sub-channels is not idle, the data will be modulated on the 80Mhz channel, but turning off the carriers corresponding to the busy sub-channel or sub-channels, here sub-channel 700-2.

Next, this information is converted into a sub-channel map representing the available sub-channels to be used for data transmission, and is included (possibly using reference thereto) in the PHY preamble 790 (shown in Figure 11 for 802.11 ax) of the data frame sent on the wireless medium.

For instance, the sub-channel map may be made of a bitmap having the same number of bits as the number of sub-channels forming the operating band (for instance 8 bits for the eight sub-channels of a 160Mhz operating band). In the bitmap, each bit indicates if the corresponding sub-channels (according to the order within the operating band) is used for data transmission, i.e. is available (bit set to 1), or not (bit set to 0).

In a variant using the BW field as defined below (corresponding to the BW field as defined in 802.11ac), the modulation band can correspond to the sub-channel configuration as defined through the BW field and the sub-channel map may be restricted to a bitmap mapping its bits on the sub-channels forming the modulation band.

The PHY preamble is modulated on a single sub-channel, namely the primary 20 MHz band (for coexistence reason with legacy devices), and it is duplicated on every idle sub-channel to be used (700-3, 700-4, 700-1) for compliance with legacy nodes that use these other sub-channels.

Next, the source node can modulate the data to be sent on the 80 MHz composite channel, while turning off the carriers corresponding to the non-available channel (according to the sub-channel map).

When the receiving node receives and decodes the PHY preamble 790 on the primary channel, it retrieves the sub-channel map (and possibly the BW field) and thus knows the width of the modulation band (80 MHz in this example) and which subchannels are used therein. The receiving node can thus demodulate the 80Mhz channel by setting the D(k) components to zero for the unused sub-channels, resulting in discarding any data carried by such unused sub-channel.

The signalling of the sub-channel map in the data frame, and more precisely in the PHY preamble 790, can be made using a map field, referred to as ACM (active channel map) field below.

Figures 9 and 10 illustrate the existing frame format of an IEEE 802.11ac PHY header used in data frames.

The 802.11ac frame format is shown in Figure 9 and starts, as expected, with a preamble or header.

The first three fields form a first header 901 and are L-STF (Short Training Field), L-LTF (Long Training Field) and L-SIG (Signal) well known by one skilled in the art when considering 802.11ac standard.

The L-STF and L-LTF fields contain information that allows the device to detect the wireless signal, perform frequency offset estimation, timing synchronization, etc. The ’L-’ stands for ’legacy’ and the details of the sequences used in these fields for the 20 MHz signals are the same as the legacy 802.11a and 802.11η preamble fields which allows for all 802.11 devices to synchronize with the wireless signal.

In addition, the L-SIG field includes information regarding the length of the rest of the frame. This means that all devices including the legacy devices will know that a frame of a given length is being transmitted.

The next fields in the frame, the names of which start with “VHT”, are specific to 802.11ac (“VHT” means 802.11ac since it stands for “Very High Throughput”) and form a VHT PHY header 902. The VHT-SIG-A field contains two OFDM symbols, namely VHT-SIG-A1 and VHT-SIG-A2.

The first symbol is modulated using BPSK, so that any 802.11η device receiving it will think that the frame is in accordance with the 802.11a frame format.

Important information is contained in the bits of these two symbols such as bandwidth mode, MCS (Modulation and Coding Scheme) for the single user case, number of space time streams, etc.

The legacy fields and the two VHT-SIG-A fields are duplicated over each 20 MHz ofthe bandwidth when 802.11ac (including the invention) is implemented.

After the VHT-SIG-A section, the VHT-STF field is sent. The primary function of the VHT-STF field is to improve automatic gain control estimation in a ΜΙΜΟ transmission.

The next 1 to 8 fields of the packet are the VHT-LTF fields, one per spatial stream (up to SS=8 usually) to be used for transmission. VHT-LTF fields allow the receiving node to calculate the multipath characteristics of the channel and apply them to the ΜΙΜΟ algorithm.

The VHT-SIG-B field is the last field in the preamble/header before the data field is sent. VHT-SIG-B is BPSK modulated and provides information on the length of the useful data in the packet and in the case of MU-MlMO provides the MCS (The MCS for single user case is transmitted in VHT-SIG-A).

Following the preamble/header, data symbols 903 are transmitted.

Figure 10 shows the VHT-SIG-A section with the number of bits used for each of its fields.

The bandwidth field “BW” 1000 is made of two bits used to indicate the composite channel bandwidth: 0 for 20 MHz, 1 for 40 MHz, 2 for 80 MHz, and 3 for 160 MHz, i.e. the modulation band as conventionally used by 802.11ac legacy nodes.

For single-user frame transmission, a partial association ID (partial AID) field is an abbreviated indication of the intended addressee of the frame, which thus enables any receiving node to enter power save mode when it ascertains that it is not the intended recipient. For transmissions to an AP (access point), the partial AID is the last nine bits of the BSSID. For a receiving node, the partial AID is an identifier that combines the association ID and the BSSID of its serving AP. A Group identifier (group ID) field was introduced in the VHT-SIG-A field. The downlink MU-MIMO transmissions can be organized in the form of MU-TXOP to facilitate the sharing of TXOP where AP can perform simultaneous transmissions to multiple receiving nodes by using the group ID. Thanks to the group ID, the nodes can determine whether they are part of the multiple-user transmission or not.

Recently document IEEE 802.11-15/0101r1 proposed a modification of the PHY preamble for the new IEEE 802.11 ax standard, which is shown in Figure 11 and is named High Efficiency PHY header (HE PHY). HE PHY comprises a first field named HE-SIG-A.

Embodiments provides that the map field to signal the sub-channel map is added to the HE-SIG preamble, in order to allow the usage of non-contiguous channel for data transmission. Of course, embodiments may apply to other header types or header formats.

Figure 12a and 12b illustrate two embodiments for such map signalling.

In the first embodiment illustrated in Figure 12a, the first three bits of the HE-SIG-A header are kept identical to the corresponding bits in the VHT-SIG-A header to keep compliance with 802.11 ac legacy nodes: the first two bits BW 1000 keep the same signification as in VHT-SIG-A (i.e. are used to specify the 802.11ac bandwidth used for modulation/demodulation) and reserved bit 1202 is now used to indicate if the data transmitted in the data frame (after the current preamble) are modulated using noncontiguous sub-channel. For that reason, bit 1202 may be named Non-Contiguous Sub-

Channel (NCSC) bit, and it signals whether or not a map field is specified within the physical layer preamble.

The map field or “ACM field” 1203 is added to indicate which sub-channels of either the operating band or the modulation band as defined in field BW 1000 are used for current data transmission.

The ACM field can directly include the sub-channel map as mentioned above. In a variant, a table of predefined sub-channel maps may be used and known at both source and receiving nodes, in which case the ACM field can store an index of an entry in such table. The ACM field thus indirectly stores the sub-channel map.

This approach advantageously reduces the number of required bits to signal the sub-channel map.

Note that the table may be limited to a restricted number of sub-channel configurations if appropriate.

These two variants are only few possibilities, while other ways to code the ACM field and the sub-channel map may be implemented in embodiments of the invention.

In the second embodiment illustrated in Figure 12b, only the ACM field (mapping the sub-channels of the whole operating band) is added to the HE-SIG-A preamble, without indicating the BW field. This is because the used bandwidth (i.e. modulation band) and the indication that the data are modulated on non-contiguous subchannel can be directly inferred from the signalled sub-channel map, i.e. from the ACM field, and thus the receiving node can know all the information.

For instance, it is easy to determine the used bandwidth (BW) using the subchannel map, which BW corresponds to the bandwidth difference between the first and last sub-channels of the map. In the same way, the NCSC indication can be determine thanks to the sub-channel map by determining whether or not all the used sub-channels are contiguous within the operating band (and more generally if the sub-channel configuration is one of the 802.11ac configurations).

This second embodiment uses lesser bits in the HE-SIG-A PHY header than the first embodiment, and also provides the sub-channel map as early as possible for the receiving node receiving the PHY preamble.

On the other hand, the first embodiment keeps a reduced compatibility with VHT-SIG-A preamble, and should preferably be used if support of non-contiguous subchannels is optional.

Figures 13a and 13b illustrate, using flowcharts, general steps of embodiments to enhance channel usage for multi-channel transmission in an 802.11ac wireless medium, from the source node’s perspective. Figure 13a focuses on the first embodiment based on the HE-SIG-A PHY header signalling of Figure 12a, while Figure 13b focuses on the first embodiment based on the signalling of Figure 12b.

The process of Figure 13a starts at step 1300 where the source node determines a first list L1 of available sub-channels from the sub-channels forming the operating band. The step may involve using the CCA mechanism to determine all the idle sub-channels ofthe operating band.

Optionally, step 1302 may consist in determining a second list of usable channels L2 that will be effectively used for data transmission. If step 1302 is not performed, list L2 is equal to L1.

Step 1302 can be performed using additional information, like interference statistics per channel or information from a negotiation that occurred prior to data transmission, to reduce the number of sub-channels of L1 to a subset forming list L2.

For instance, sub-channels on which history data show interference statistics below a predefined threshold are kept in list L2.

Next step 1340 consists in determining whether or not the receiving node support usage of non-contiguous sub-channels, i.e. supports transmission over noncontiguous sub-channels within the operating band. More generally, step 1340 checks whether or not the receiving node supports transmission over a subset of sub-channels different from the sub-channel configurations allowed by the operating mode of the wireless network, for instance by 802.11ac.

Step 1340 can involve analyzing the capabilities of the receiving node. The receiving node’s capabilities are for instance sent in each beacon frame and during the prior association phase of the nodes with an access point (AP).

If it is determined, at step 1340, that the receiving node does not support non-contiguous channel usage, step 1350 is executed. Otherwise (the receiving node does support such usage) step 1360 is executed.

The branch ofthe process starting from 1350 is a slight adaptation of current 802.11ac process to the signalling of Figure 12a.

At step 1350, the source node determines a third list L3 of available contiguous channel from among list L1, using the IEEE 802.11ac standard fallback procedure as described above with reference to Figures 3a, 4 and 5. List L3 forms the operable composite channel to be used for data transmission, i.e. the modulation band to be used.

During step 1350, the value for BW field 1000 is set with the width of the modulation band corresponding to the composite channel thus determined.

Next, at step 1351, the value for NCSC field 1202 (having a Boolean value) is set to 0 to indicate that the used composite channel is entirely contiguous within the operating band.

Step 1352 is optional since ACM field 1203 will not be taken into account given the setting of NCSC field to 0 (and thus not be used by the receiving node). In this step, default content for ACM field 1203 is obtained (for instance a default index or default values for the bitmap).

Next, at step 1353, the values for ACM, NCSC and BW fields are inserted in the TX_VECTOR used as an argument in the PHY primitive, to configure the PHY layer before data transmission.

Compared to 802.11ac standard, the values for ACM and NCSC fields are added for the sake of this invention to support non-contiguous sub-channel usage.

During step 1353, an HE_PHY preamble (as described above with reference to Figures 11 and 12a) is built by the PHY layer using the values passed by the TX_VECTOR.

Next, at step 1354, the PHY layer modulates the created HE_PHY preamble on a 20MHz band and sends it on every 20MHz sub-channel of the used composite channel.

Next, at step 1355 and similarly to 802.11ac, the PHY layer modulates the data to be transmitted on the modulation band corresponding to the used composite channel, i.e. on the modulation band that encompasses the contiguous sub-channels forming L3, and then sends the data on the composite channel.

The branch of the process starting from 1360 is more specific to the invention since it allows usage of non-contiguous sub-channels using the signalling of Figure 12a. This branch is executed if step 1340 determines that the receiving node supports usage of non-contiguous sub-channels.

At step 1360, a value for ACM field 1203 is built, representing list L2 of subchannels to be used for data transmission.

As mentioned above, building the value for ACM field 1203 may for instance consist in selecting a corresponding index from a table of bitmaps, or by directly creating the bitmap. In step 1360, the bandwidth BW corresponding to the width of the modulation band is determined. The modulation band should be at least wide enough to include all the sub-channels listed in list L2, i.e. identified in the ACM as sub-channels to be used. Typically, this modulation band can be the band resulting from the concatenation of all the sub-channels of the operating band between the first and last sub-channels of list L2 (and including these two first and last sub-channels).

Next, at step 1361, the value for NCSC field 1202 is set to 1 to indicate that the data following the preamble will be transmitted over a non-contiguous composite channel, i.e. on sub-channels that are not contiguous within the operating band and within the modulation band.

Next, step 1362 is similar to step 1353 to pass NCSC, ACM and BW values to the PHY layer using the TX_VECTOR, and to create (by the PHY layer) the corresponding HE_PHY preamble.

As step 1363, the PHY layer modulates and sends the HE_PHY preamble only on the used sub-channels of list L2, i.e. on the sub-channels as mentioned in ACM field of the HE_PHY preamble.

Next, at step 1364, the PHY layer sends the data on the sub-channels of L2 using for instance a modulation on the BW band turning off the carriers (OFDM tones) corresponding to the unused sub-channels in the modulation band (i.e. not used according to the ACM map). This modulation may involve the formula, as mentioned above,:

where N is the FFT size.

To turn off the carriers of non-active sub-channels, the D(k) components for these unused sub-channels are set to 0. Since the unused sub-channels are defined in ACM field 1203 (as those sub-channels of the modulation or operating band that are not used for data transmission), the bitmap of ACM field 1203 may be used as a filter for modulation.

Still at step 1364, the modulated signal is sent on the wireless network.

Once step 1355 or 1364 is performed, the process ends. The data frame so transmitted is processed by the receiving node as described below with reference to

Figure 14.

Regarding the second embodiment for signalling the usage of noncontiguous sub-channels illustrated through Figure 12b, the process of Figure 13b is an adaptation of the one of Figure 13a wherein steps 1351, 1352 and 1361 of Figure

13a are deleted (since the NCSC field doesn’t exist anymore), and an additional step 1356 (between steps 1350 and 1353) is added.

In addition, since the NCSC and BW fields are no longer used, steps 1353 and 1362 only provide the value for ACM field 1203 to the PHY layer.

In this embodiment, ACM field 1203 provides a sub-channel map mapping its bits on all the sub-channels composing the operating band.

The other steps are similar to the corresponding ones (with same numeral reference) of Figure 13a.

For the invention to comply with receiving nodes that only supports 802.11ac sub-channel configurations (i.e. “no” at test 1340), additional step 1356 (after having determined the contiguous 802.11ac composite channel to be used) sets the value of ACM field 1203 to be representative of list L3. This is for instance performed by selecting a corresponding index from a table of bitmaps (which table should thus contain all the sub-channel configurations as allowed in 802.11ac) or by creating the corresponding bitmap for instance.

This bitmap is used by the PHY layer to modulate the data on the appropriate contiguous composite channel (step 1355).

In case non-contiguous sub-channels are used, the source node only builds and transmits ACM field 1203 to the receiving node, for the latter to obtain the subchannel map.

As for Figure 13a, the modulated signal transmitted on the wireless network is received and processed by the receiving node as now explained with reference to

Figure 14.

The process at the receiving node starts at step 1400 in which it demodulates the HE_PHY preamble received on the primary channel (in the meaning of 802.11ac, i.e. the channel on which the contention process [backoff] by the source node has been performed). The receiving node then retrieves therefrom the information embedded in the HE-SIG-A preamble.

At step 1410, the receiving node determines the bandwidth BW of the composite channel that will be used for the data transmission by the source node (this step is performed before the data are received), i.e. it determines the modulation band from which the received signal must be demodulated.

Step 1410 can be done by reading BWfield 1000 ofthe HE-SIG-A preamble (for the first embodiment) or by recovering and analyzing the content of ACM field 1203 (for the second embodiment). In the latter case, the bandwidth can be determined by reading the index referring to the table of bitmaps and thus obtaining the corresponding bitmap, or by analyzing the ACM bitmap directly inserted in field 1203. The bandwidth corresponds to the width between the first and the last sub-channels in the bitmap.

Of course, other ways to signal the modulation band can be implemented in combination with the sub-channel map indicating which sub-channels of the modulation band are used for data transmission.

Next, at step 1420, the receiving node determines whether or not the source node uses a non-contiguous composite channel for data transmission. This determination step can be performed by checking NCSC field 1202 if any (for the first embodiment), or by analyzing the ACM value (looking for “hole” in the bitmap for the second embodiment).

If step 1420 determines that a contiguous composite channel is about to be used by the source node, step 1430 is executed in which the PHY layer is configured to demodulate the signal received from the contiguous composite channel as currently done in the IEEE802.1ac standard. Next, upon reception, the data are actually demodulated.

If step 1420 determines that a non-contiguous composite channel is about to be used by the source node, step 1440 is executed in which the PHY layer is configured to demodulate a data signal from the modulation band (BW) and to retrieve the data from the non-contiguous composite channel within the modulation band (i.e. from the used sub-channels).

This may involve demodulating the signal received on the whole BW band (BW can be retrieved directly from the preamble or deduced from the ACM field) and filtering the demodulated signal using ACM field 1203 to discard the data from the nonactive sub-channels. Again, the formula as reproduced above can be used for demodulation, wherein the D(k) components for unused sub-channels are set to zero.

Thanks to test 1420, the receiving node uses the sub-channel map (signalled in the ACM field) to demodulate data only if the signalling NCSC flag is set to indicate a map field is specified in the HE-SIG-A preamble.

Next to steps 1430 and 1440, step 1450 is executed in which the demodulated (and non-discarded where appropriate) data are sent to the MAC layer for further processing as conventionally done.

This ends the process.

Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications will be apparent to a skilled person in the art which lie within the scope of the present invention.

Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention, that being determined solely by the appended claims. In particular the different features from different embodiments may be interchanged, where appropriate.

In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used.

Claims (21)

1. A communication apparatus comprising: determination means for performing carrier sensing on a successive plurality of sub-channels to thereby determine an available sub-channel to be used to transmit data; and transmission means for transmitting to another apparatus, a physical layer preamble of data to transmit, the physical layer preamble including information related to a sub-channel that is not available for performing data transmission based on a result of the determination obtained by the determination means.

2. The communication apparatus of Claim 1, further comprising storing means for storing the information in the physical layer preamble of data prior to transmission.

3. The communication apparatus of Claim 1, wherein the transmission means are further configured for transmitting data to the other apparatus, said transmitting including modulating the data on a modulation band encompassing two or more available sub-channels as determined by the determination means.

4. The communication apparatus of Claim 3, wherein the two or more available sub-channels are made of sub-channels that are not contiguous within the successive plurality of sub-channels.

5. The communication apparatus of Claim 3 operable on a wireless network, wherein an operating mode ofthe wireless network defines a restricted number of predefined sub-channel subsets that are available for reservation by any wireless node of the wireless network to transmit data, the predefined sub-channel subsets being made of contiguous sub-channels within the successive plurality of sub-channels, and the two or more available sub-channels encompassed by the modulation band form a sub-channel subset different from any predefined sub-channel subset.

6. The communication apparatus of Claim 5, wherein the operating mode of the wireless network is according to the 802.11 ac standard, and the restricted number of predefined sub-channel subsets is made of 20MHz, 40MHz, 80MHz and optionally 160MHz contiguous bandwidths within the successive plurality of sub-channels.

7. The communication apparatus of Claim 3, wherein the two or more available sub-channels are made of sub-channels that are contiguous within the operating band.

8. The communication apparatus of Claim 1, wherein a map field in the physical layer preamble includes a sub-channel map defining available sub-channels for performing data transmission and the sub-channel that is not available for performing data transmission.

9. The communication apparatus of Claim 8, wherein the map field includes a map identifier identifying an entry of a table of maps.

10. The communication apparatus of Claim 8, wherein the map field starts a HE-SIG-A header in the physical layer preamble in accordance with the 802.11ax standard.

11. The communication apparatus of Claim 1, wherein performing carrier sensing includes using a clear channel assessment mechanism to sense available subchannels within the successive plurality of sub-channels.

12. The communication apparatus of Claim 1, wherein performing carrier sensing includes determining a first set of sub-channels that are sensed idle within the successive plurality of sub-channels and reducing the first set to a set of available subchannels to perform data transmission.

13. The communication apparatus of Claim 1 wherein the transmission means are further configured for modulating the physical layer preamble on a primary sub-channel determined as available based on a result of the determination and duplicating the modulated preamble on a secondary sub-channel determined as available based on a result of the determination.

14. The communication apparatus of Claim 3, wherein the transmission means are further configured for modulating the data on the modulation band by turning off one component of a modulation scheme that correspond to the sub-channel that is not available.

15. The communication apparatus of Claim 14, wherein the transmission means are further configured for transmitting the information related to the sub-channel that is not available from a MAC layer to a PHY layer of the communication apparatus, using a MAC-PHY interface, to configure the PHY layer with the information for the PHY layer to perform modulation on the modulation band.

16. The communication apparatus of Claim 15, wherein the information is passed to the PHY interface as a parameter of a PHY primitive.

17. The communication apparatus of Claim 3, wherein the modulation band is made of all the sub-channels of the successive plurality of sub-channels from the first sub-channel determined as available by the determination means to the last subchannel determined as available by the determination means.

18. The communication apparatus of Claim 3, wherein the modulation band is the successive plurality of sub-channels.

19. The communication apparatus of Claim 1, further configured to, prior to performing carrier sensing, determining whether or not the communication apparatus supports transmission over a subset of sub-channels different from predefined subsets or supports transmission over non-contiguous sub-channels within the successive plurality of sub-channels.

20. A method of communicating comprising: performing carrier sensing on a successive plurality of sub-channels to thereby determine an available sub-channel to be used to transmit data; and transmitting to another apparatus, a physical layer preamble of data including information related to a sub-channel that is not available for performing data transmission based on a result of the determination obtained by the determination means.

21. A non-transitory computer-readable medium storing a program which, when executed by a microprocessor or computer system in a communication apparatus, causes the apparatus to perform the method of Claim 20.